A respiratory assistance device typically comprises a housing provided with a blower or the like arranged to blow gas along a delivery conduit to a patient interface at the face of a patient. The patient interface may comprise a full or partial face mask, or a nasal cannula, for example. Gas, typically air or oxygen enriched air for example, is driven along the delivery conduit to the patient interface to increase the pressure in the airway of the patient. This can assist with the breathing of the patient, and may be used in treatment of sleep apnoea for example.
It can be desirable to control the humidity of the gas delivered to the patient and in that instance a humidifier may be provided, either as part of the respiratory assistance device, or elsewhere along the gas flow path. The humidifier typically comprises a chamber arranged to be filled or partially filled with a liquid, usually water, and a heating plate underneath the chamber. The water is vaporised by the heating plate, and the water vapour passes into the stream of gas being delivered to the patient to humidify the gas.
The use of an electric heating plate, or heating coil or the like, increases the energy consumption of the device. Such an arrangement is not typically able to react quickly to changes in the desired humidity since it is necessary to heat the entire body of water in the chamber to generate water vapor, also resulting in a lag between the humidifier being switched on, and water vapour being delivered to the gas stream. Furthermore such an arrangement is relatively unwieldy in terms of size, shape, and where it can be located. Yet further, the increased temperature inside the chamber means that the chamber walls must be configured to withstand such temperatures. There are also safety implications associated with a heated body of water.
In a paper entitled ‘Solar Vapor Generation Enabled by Nanoparticles’ published 19 Nov. 2012, the entire contents of which are incorporated by reference, Neumann, Urban, Day, Lal, Nordlander and Halas have described the generation of water vapours by illuminating metal or carbon nanoparticles dispersed in a body of water. Light energy is directed onto the nanoparticles which absorb the light energy and convert some of it to heat. The heated nanoparticles heat the water in the region around each particle, generating water vapour around each particle. The water vapour passes up through the body of water and is released as steam.